Repositioning hollow hidden log, lay back comfortably (2,1,4,5)
I believe the answer is:
by a long chalk
'comfortably' is the definition.
(I've seen this before)
'repositioning hollow hidden log lay back' is the wordplay.
'repositioning' indicates an anagram.
'hollow' says to hollow out the word (remove centre letters).
'hidden' with its middle removed is 'hn'.
'hn'+'log'+'lay'+'back'='hnloglayback'
'hnloglayback' anagrammed gives 'BY A LONG CHALK'.
(Other definitions for by a long chalk that I've seen before include "To a considerable distance or degree" , "comfortably" .)